1. Field of the Invention
The present invention relates to a vehicle front wheel suspension construction and more particularly to an idler arm structure and improved bearing assembly for use in the wheel suspension construction.
2. Background of the Invention
In conventional application, the idler arm of a steering linkage is ideally pivotally mounted on vehicle superstructure in such a way as to provide free rotation about a fixed axis. For optimum geometric accuracy, the bearing which establishes the axis of rotation should completely resist any tendency of the idler arm to deflect in any plane other than one normal to the axis of a fixed pivot. Performance factors typically analyzed for the idler arm joint include torque, lash, and long term durability. The torque of an idler arm joint, commonly referred to as functional torque, is the torque necessary for pivoting the idler arm about the support. Lash is the axial movement of the idler arm relative to the support while durability deals with the normal tendency of an idler arm joint to wear in use such that a degree of slackness gradually arises which tends to reduce the accuracy of the steering geometry.
Attempts have been made to utilize plastic bearings in the idler arm joints. One common problem with the plastic bearings is the loss of press-fit which leads to premature wear, lash, and sealing problems. The tendency for plastic to creep under stress causes the loss of the press-fit. The stress is caused by steering loads and by the press-fit itself.
The use of compression springs to take up axial lash has also been utilized in prior idler arm joints. The main problem with using springs to take up axial lash is obtaining a spring that is stiff enough not to deflect under loading, but forgiving enough to provide consistent torque. Another problem exists in locating a bearing surface for the spring.
Other attempts have been made at using a nut and a corresponding assembly torque to axially de-lash an idler arm joint. This method has been proven both analytically and experimentally very difficult to control torque. This is in large part due to the small variations in nut assembly torque which cause large variations in functional joint torque. Another problem with this method is nut retention. The nut assembly torque must be very low in order to maintain low idler arm functional torque. Since the assembly torque is too low to generate the proper thread stress and clamping forces, additional means of maintaining nut retention need to be added. This leads to very complicated designs.